This invention relates to recording and reproducing optical disk devices, and more particularly to magneto-optical disk devices which utilize a magnetic material as the recording medium.
The recording and reproducing optical disk devices of the above type effects recording on the disk as follows: the recording spot on the disk is heated by means of a light (laser) beam to raise the temperature thereat; in addition, a varying exterior magnetic field, namely the biasing magnetic field, is generated by a magnetic head to reverse the direction of the magnetization of the magnetic material on the disk. On the other hand, during the reproducing operation, a light beam of less energy is irradiated on the recording surface to read out the above direction of the magnetizion on the disk by means of a magneto-optical effect, such as the magnetic Kerr effect or Faraday effect. This type of optical disk device is finding increasing applications as exterior memory devices of computers, audio disks, etc.
FIG. 1 shows an example of the recording and reproducing optical disk device of the above type. A disk 1 is rotated by a disk driver motor 2. The light beam 4 emitted from the optical head 3 forms a converged light spot 5 on the surface of the disk 4; the diameter of the light spot 5 is generally from about 1.0 to 1.5 micrometers. The optical head 3 comprises following elements: a light source for emitting the light beam; optical elements for conducting to the surface of the disk 1 the light beam emitted from the light source; optical elements for conducting the light reflected from the disk surface; a photosensor element (a light-sensitive detector) for converting the reflected light into an electrical signal upon receiving the reflected light via the above optical elements for conducting the reflected light; and optical sensors for detecting the focusing and tracking errors of the light spot 5 on the recording surface of the disk 1. The objective lens of the optical head 3 which forms the light spot 5 on the disk 1 is driven in the focusing direction perpendicular to the recording surface of the disk 1 and in the direction perpendicular to the track on the recording surface, such that the focusing and the tracking errors are reduced. The optical head 3 is supported on the base 6, which is supported on the frame of the device via the bearings 7a and 7b to be driven in the radial direction A. Further, on the base 6 is disposed a magnetic head 8 for generating an exterior magnetic field from the side opposite to the side at which the optical head 3 is situated. The recording on the disk 1 is effected by modulating this exterior magnetic field generated by the magnetic head 8.
As shown in detail in FIG. 2 (a) through (c), the distance (designated by H.sub.1 through H.sub.3, respectively) between the recording surface of the disk 1 and the magnetic head 8 varies as the disk 1 rotates. The strength of the magnetic field generated by the magnetic head 8 is generally from about 100 to 500 Oe at the recording surface; as illustrated in FIG. 3, the magnetic field strength B at the recording surface of the disk 1 (plotted along the ordinate) decreases as the distance H between the surface of the disk 1 and the magnetic head 8 (plotted along the abscissa) increases. The distance H between the recording surface of the disk 1 and the magnetic head 8 varies as the disk 1 rotates, due, for example, to an undulating motion of the recording surface of the disk 1.
The above conventional recording and reproducing optical disk device therefore has the following problems. First, the distance H between the magnetic head 8 and the recording surface of the disk 1 cannot be set as small as is desired, if the contact of the head 8 with the disk 1 is to be avoided; thus, the efficiency of the magnetic head 8 in producing a magnetic field at the recording surface of the disk 1 is reduced. Second, the variation of the distance H between the head 8 and the recording surface of the disk 1 results in a variation in the recording characteristics. Third, if the above problems are to be avoided, an extremely high mechanical precision is required of the device.